We are using neovascularization as a novel method of identifying neoplastic transformation at a very early stage in the human mammary gland. Biopsy specimens are removed at surgery and transplanted immediately to the rabbit iris or cornea. Neovascularization is monitored with a slit-lamp stereomicroscope. The objective is to delineate the progression of malignant transformation both a) topographically, by assaying the tissue around a known carcinoma and b) temporarily, by studying histologically benign, premalignant lesions of the human breast.